Until now, in view of the generation of electric fields in high tension electricity lines, the performance of construction and maintenance services on such lines, such as cleaning and repair services, substitution or installation of any equipment, has been very difficult.
One safe way to perform these services is to turn the electrical power off putting the installations and the lines out of service. However, this may result in economic loss to the consumers and is not always feasible or possible, and even if possible, it will undoubtedly cause serious operational difficulties to the consumers.
Additionally, in particular cases such as when the lines traverse a river or other waterway, it is not possible to perform the desired services even if the electricity is disconnected.
One manner to perform maintenance and repair servicing of high tension electricity lines without any interruption of the electricity is to provide the operator performing the servicing with electrically conductive equipment (e.g., conductive clothes, gloves, stockings and boots). With such equipment, the operator may be in contact with the energized high tension wire and will consequently maintain the same potential as the line. The operator after climbing the tower, may travel along the line using insulated canes, hooks and other appropriate fixing elements. It is a drawback that this method is quite slow and carries a certain risk to the operator when he pass from the neutral pole (the tower) through the high tension positive pole (the wires) and requires the operator to be in almost perfect physical condition.
Another way to perform maintenance and repair services in high tension towers and wires entails positioning the operator, equipped with electrically conductive clothes, inside a cabin suspendable by a crane or similar suspension device, raising the cabin via a crane, and placing it adjacent to the line to be repaired. The cabin is electrically connected to the line thereby providing no potential difference between cabin and the operator. Likewise, the crane would be isolated from earth and equally electrically connected to the line so that in the same way, there is no potential difference. It is a disadvantage of this method that many times, the maintenance services are to be performed in remote areas where access to vehicles, like cranes and other similar equipment, is not available. Furthermore, this method entails severe risks to the operator if the isolation/insulation between the equipment and the ground fails or is insufficient.
Recently, a technique has been developed which uses a helicopter provided with a platform to carry the operator directly to the place where the repair or maintenance services are required, e.g., in the tower or the high tension line. In this case, the platform is mounted directly to the helicopter landing gear and is electrically connected to it. The operator wears electrically conductive equipment which is electrically connected to the platform. The helicopter carries the operator to the line to be repaired, and stays adjacent to it in a "repair position". The operator is coupled by himself to the power line so that the line, the operator, the platform and the helicopter maintain the same potential. Additionally, the pilot of the helicopter wears electrically conductive equipment which is suitably connected to the helicopter.
In this case, since all of the elements are connected to one another and are at the same potential, when the helicopter stops in the air, there is no electric path through the earth and consequently there is no risk of any electrical discharge over the operator, who is thus able to perform the maintenance services calmly and safely.
At the present time, there exist cabins arranged on the edges of a structure mounted in the helicopter which carry the operator until he or she is positioned on or close to the high tension line to be repaired. These cabins are able to be additionally transferred to the high tension line through appropriate sheaves. In this manner, the maintenance service could be performed when the helicopter is proximate to the high tension line, or the cabin may be transferred to the line and then uncoupled from the helicopter's structure, allowing the helicopter to separate itself from the high tension line and to perform other tasks while the operator is performing the maintenance services on the line. When this operation is finished, the helicopter comes back and the cabin is hooked again at the edge of the structure mounted in the helicopter and uncoupled from the high tension line.